The present invention relates to the use of curable, particularly ultraviolet light (UV) curable, compositions as fillers for porous substrates, particularly wood-based porous substrates, to render them smooth and suitable for further processing.
Porous substrates derived from wood such as particleboard, chipboard, composition board, as well as paper products, generally have a wide range of porosity, absorbancy, and microscopic and macroscopic surface irregularities as compared to, for example, glass and metal substrates. On a microscopic level, they present a random array of peaks and valleys and also roughness due to the presence of fibers in the surface. Such characteristics of these substrates generally make them unsuitable for the efficient application of decorative topcoating compositions directly to the substrate where a smooth appearance is desired. Such wood based, topographically irregular, substrates often are coated with compositions typically referred to as "fillers" to help provide a smooth surface.
However, the porosity and topographical irregularities of such substrates also make the efficient application of filler compositions itself difficult. For example, if the filler is substantially absorbed by, or "drunk in" by, the substrate, the surface irregularities in the substrate remain. When such substrates are warm or hot, for example after particleboard is removed from a press during manufacture, they tend to drink in the filler composition even more. Moreover, this problem can be compounded by the loss of more volatile components from the filler composition while it is in contact with the warm or hot substrate before it hardens or cures. Thus, the absorption of the filler composition by the substrate results in inefficiency of production as well as undesirable appearance imperfections in the final product.
The present invention is directed to alleviating these problems through the use of a specially formulated composition, preferably one which is curable by exposure to ultraviolet light.